The proposed research consists of several projects designated to elucidate the nature of immune complexes in sera of patients with malignancies: 1. Sera of patients with neoplastic diseases will be examined for presence of immune complexes by the Raji and conglutinin assays. 2. Attempts will be made to isolate serum immune complexes using Raji cells, conglutinin-Sepharose or staphylococcal protein A-Sepharose as in vitro adsorbents. 3. Peripheral mononuclear cells from patients with leukemia will be analyzed for in vivo bound immune complexes and anticellular antibodies. Antibodies recovered will be used for attempting to isolate the cell surface antigens to which they are directed.